1952 Merury Overdrive

I have had a discussion about this a few years ago, but am having a new problem.

I have a 1952 mercury and I am curious if when I’m going to stop or slow down if I need to take it out of overdrive before doing so. The overdrive relay does not work in this car so I rigged up a switch that I can use to turn the overdrive on after reaching about 30 mph. I do turn it off before stopping or slowing down.

Now when I get above 30 mph and turn on the switch to engage the overdrive, it rarely shifts into the overdrive gear.

The last time it worked I hit a hard bump on a gravel road which cause the car to die, but after that until I shut the car off, the overdrive seemed to engage.

Could it be a connection issue? When I have the car running and parked and turn the switch on for the overdrive I can hear it click.

Any thoughts would be appreciated!


Here is a link to how the overdrive in your Mercury works. This may help you diagnose your problem.

Wish I could help. Would love to see some pictures of it though!

As I understand the overdrive, there is a cable that locks out the overdrive when pulled out, but allows the overdrive to operate when pushed in. The overdrive is electrically controlled. If the overdrive cable is pushed in, the car is in free wheeling–it coasts without any braking from the engine. There is a governor which then allows the overdrive gear to kick in after the car reaches 28 mph. When the overdrive gear engages, the free wheeling goes away. However, when the car speed drops below 28 mph, the overdrive gear disengages and the car goes back to free wheeling.
First, pull the cable out (with your switch off) and feel the engine braking. Now, push the cable in and leave your switch off. Does it feel different? If so, the cable is allowing the overdrive to engage. If not, check that the cable is working.
Now, speed up to about 35 mph with the cable pushed in, flip your switch and release the accelerator. You should feel a slight bump if the overdrive engages.
I really think you should find a replacement relay instead of using the switch. You may be bypassing the governor which is essential for proper overdrive operation.

You will have to excuse me as my memory of the operation of the overdrive is a little hazy.

IIRC, with the lock out knob pushed in; you accelerate to about 30 and then lift the accelerator and the unit would shift into overdrive. Below the governor speed, you would get freewheeling. To force the unit out of overdrive, you would floor the accelerator and the unit would go into direct until you lifted the pedal again. If you wanted to lockout the overdrive at this point, you could pull out the lockout knob again.

Several things may be wrong with your unit (I assume it is the Borg Warner). The solenoid plunger or the pawl may be stuck i.e. gummed up. Also the balk ring may not be providing enough drag from the sun to clear the ring away from the pawl i.e when you lift the accelerator the friction of the pawl resting on the balk ring is enough to turn the ring.

To answer your original question, if you can get the car moving with it still in overdrive i.e. breakaway in 1st overdrive satisfactorily, you could leave it in overdrive. It will be more strain on the clutch and the overdrive planets. You won’t have freewheeling and engine braking will be a little less. I knew someone with a 1961 Chevy that had your switch arrangement. The 3 speed gear box was split into a 6 speed i.e 1st, 1st overdrive, 2nd, 2nd overdrive, direct, overdrive. He was a wizard at driving a 4 speed nonsyncronized transmission with split rear axle dump truck–loaded–talk about triple clutching.

http://www.dacoglu.com/desotoCD/11A_ThreeSpeed With Overdrive/Borg Warner Overdrive Transmission.doc
Here is another link to the overdirve transmission with a picture showing the internal working parts.
Hope this helps.

Thanks everyone for your input. The overdrive has been working for the most part today!

As to the cable to lock-out or enable overdrive. I replaced this, but the cable does not function as it should. I wonder if it’s possible that sometimes while driving the handle on the transmission for overdrive moves just slightly thus not allowing the overdrive to engage. Hopefully it keeps working for me. The car just purrs right along once in overdrive. Otherwise the engine is quite loud.

When the Borg-Warner overdrive is working correctly, it is a great transmission. The Willys Jeep station wagons that came out in 1946 right after WWII came with this transmission as standard equipment because the “Go-Devil” 4 cylinder engine would scream at anything over 50 mph in direct drive.
In order not to damage the overdrive unit, for which parts may be hard to obtain, I would recommend checking the cable and get it to function properly and get a new relay and remove the bypass switch.

Any ideas where I could get a new relay? I agree that it is wonderful when this unit works correctly.

Back to the 50’s in St. Paul this weekend. 12,000 cars 64 and older. Lots of Fords and Mercs and people that know about them and lots of vendors with parts. Even a Morris Minor or two.

I would try to replace the relay with OEM if possible but heavy duty 12VDC relays are available everywhere. Just check with a major auto parts store or go online. I’ve included a picture of one which might be overkill but it should work for your application.